1. Field of the Invention
This invention relates to analog signal conditioning and more particularly to the removal of parabolic phase distortion from high frequency signals using a pair of series connected transversal filters.
2. Description of the Background Art
In high frequency transmission systems, it is well known that waves of different frequencies do not propagate at the same velocity. (Ramo, Whinnery, and Van Duzer, Fields and Waves in Communication Electronics, 2nd ed., 1984, pp. 396-399.) In the transmission of a broadband microwave signal through a waveguide, the higher frequency signals travel at a higher group velocity than the lower frequencies. The staggered arrival of various signal components at a final destination gives rise to group delay distortion. Group delay distortion is defined as the negative change in phase with respect to frequency. Linear group delay corresponds to parabolic phase distortion. This distortion can be corrected using a suitable delay network which slows down the faster components. However, the compensation required varies with frequency, and satisfactory results over a range of frequencies are generally difficult to achieve.
Various approaches to equalizing this so-called "delay distortion" have been proposed. In U.S. Pat. No. 3,253,238, Woo discloses the use of a waveguide containing an internal variable pertubation in the form of a conducting rod mounted at an angle with respect to the waveguide centerline.
A significant improvement in the art of equalization was provided by the development of the transversal filter equalizer, providing a way to compensate for both channel amplitude and phase distortion. U.S. Pat. No. 3,829,798 by Byram et al. discloses an equalizer comprising a series of cascaded transversal filters, each with multiple taps to form an all-pass network.
During a preliminary search of the art related to transversal filters, a number of additional patents were identified which deal primarily with digital filters or analog magnitude filters. These patents are identified as follows:
______________________________________ 3,292,110 Becker et al. 3,727,136 Schroeder et al. 3,860,892 Speiser et al. 4,258,340 Ryu 4,607,241 Horowitz 4,757,516 Yoshimoto et al. ______________________________________